Abstract <p>The influence of nanoscale iron supported on biochar (nFe/BC) in the transport and retention of hexavalent chromium (Cr(VI)) has gained considerable attention. The current study aimed to investigate the transport and retention of Cr(VI) with nFe/BC in the absence and presence of humic acid at pH of 5.0-9.0 in water-saturated soil columns. Our results showed that nFe/BC clearly inhibited the transport of Cr(VI) (Cr(VI) mass recovery = 3.76%) in a soil column, compared to the individual transport of Cr(VI) (19.9%). This was possibly because a large amount of Cr(VI) could be reduced to Cr(III) by nFe/BC during cotransport, and the resulting Cr(III) was adsorbed onto retained nFe/BC or soil. Moreover, the retained Cr in soil columns was mostly dominated by the form of Cr(III). Increasing solution pH facilitated the cotransport of Cr(VI) with nFe/BC in soils, likely because the negative charge density on the surface of nFe/BC increased with an increase in pH, leading to an enhanced electrostatic repulsion between Cr(VI) and nFe/BC. Humic acid promoted the transport of Cr(VI) in soils, likely because of the competition between Cr(VI) and humic acid for available retention sites on the surface of nFe/BC or soil. Our findings indicate that nFe/BC could be an efficient material for remediation of Cr(VI)-contaminated soil, and highlight the important effects of HA and solution pH on the transport and transformation of Cr(VI) with nFe/BC in a subsurface environment.</p> Graphical Abstract <p></p>